Apparatus for detecting hydrogen embrittlement



E. scHAscHL 3,102,419

APPARATUS FOR DETECTING HYDROGEN EMBRITTLEMENT Sept. 3, 1963 Filed Nov.18. 1960 INVEN TOR.

EDWARD SCHAS'CHL United States Patent 3,102,419 APPARATUS FOR DETECTINGHYDROGEN EMBRITTLEMENT Edward Schaschl, Crystal Lake, 111., assignor toThe Pure This invention relates to a device for determining theembrittling or intercrystalline-crack-producing characteristics ofvarious fluids, such as crude petroleum.

Serious difliculties from embrittlement in oilfield apparatus, pressurevessels, and chemical-processing equipment have been encountered. Theprior art has recognized the embrittlement problem chiefly in relationto boiler operation, wherein it was noted that while water in a boilerseldom contains a sufficient concentration of deleterious materials toproduce embrittlement problems, should the deleterious materials becomehighly concentrated by evaporation, the boiler water can produceembrittlernent cracks and failures in steel which is maintained understress in contact with such concentrated solutions. The prior artaccordingly developed methods and techniques for artificiallyconcentrating various materials in boiler water and determining thepropensities of such concentrated solutions to produce cracks underconditions of stress.

It is now known that other chemical agents produce embrittlernentcracking to a much greater extent than does boiler water. The prior arttechniques for evaluating the embrittling propensities of various fluidshave proved unsatisfactory because of the need to produce artificiallysevere concentrations of the deleterious agent, or because the deviceswere too insensitive to produce meaningful results within a reasonableperiod of exposure to fluids which were not artificially concentrated.When concentrated solutions are used, the information thereby obtainedcannot readily be extended or interpreted to produce meaningfulestimates of the likelihood of embrittlernent failure of parts contactedby fluid which is not so concentrated.

Certain conditions which occur in oil wells and oilprocessing equipmentpromote the failure of ferrous alloys by a phenomenon known as hydrogenembrittlement. Actual failure occurs in the form of smooth cracks,similar in appearance to hacksaw cuts, when the ferrous-alloy object orstructural member is subjected to stress. Even mild corrosion in thepresence of certain sulfur compounds may cause hydrogen embrittlement offerrous alloys and resulting failure when the alloys are stressed abovespecific critical values. It is recognized in the art that each ferrousalloy has a critical stress level at which failure will occur afterhydrogen embrittlernent has taken place, and that the time required forhydrogen embrittlement is dependent upon the characteristics of theenvironment. However, heretofore there have been no adequate means oftesting the effects of various fluids on the failure of ferrous alloys.

It is an object of this invention to provide a simple test apparatus todetermine the resistance of various ferrous alloys to hydrogenembrittlement when exposed to particular environments. Yet anotherobject of this invention is to provide a test device for determining thecritical stress at which hydrogen-embrittlement failure will occur uponexposure to a particular embrittling fluid. This invention in part stemsfrom the discovery that stressed coil springs are peculiarly susceptibleto hydrogen embrittlement, and that ferrous springs, when tensioned andexposed to an embrittlement producting fluid, will fail in a muchshorter perior of time than will conventional stressed structures.

Broadly, the device of this invention comprises a metal Patented Sept.3, 1963 "ice test specimen in the form of a ferrous spring, means fortensioning the spring and supporting it in exposure to a fluid to betested, and means for indicating the failure or breaking of the spring.In use, a preselected stress is applied to the spring, the assembly ispositioned in the environment under study, and the length of timerequired for the spring to fail is noted. Sequential tests may be madeat increasing stresses to determine the critical stress of the metalalloy under study, or, alternatively, a stress at least equal to thecritical stress may be applied to the spring and other test conditionsmay be altered, as by adding embrittlement inhibitors to the fluid understudy,

or altering the composition of the fluid.

This invention is best decribed with reference to the drawings, ofwhich:

FIGURE 1 is a frontal, sectional, view of a test device constructed inaccordance with this invention.

FIGURE 2 is a view in the direction 2-2 of FIG- URE 1.

FIGURE 3 is a right side view of the flag assembly of FIGURE 1.

FIGURE 4 is a sectional view of a portion of an alternate deviceconstructed in accordance with this invention.

Referring to FIGURE 1, base 10, which may be a bull-plug, supportsperforated, projecting, support-member 12, which is of tubularcross-section, and is rigidly secured to base 10 by threads 14.Support-member 12 is provided with perforations such as perforations 13.The projecting end 16 of the tubular support-member is threaded at .18to accept end-plug 20.

End-plug 24? includes an axial hole 22 through which extends eye-bolt24. Nut 26 limits the upward movement of eye-bolt 24, the downwardmovement being limited by the striking of the head of the bolt againstplug 29. Eye-bolt 24 may be provided with a flat area on one sidethereof, to mate with a corresponding flat area in hole 22, therebypreventing rotation of the eyebolt as nut 26 is rotated.

. Eccentric shaft 28 passes transversely through base 16, which baseincludes a hollow portion 30 within its cup-shaped configuration.Eccentric shaft 28 is sup ported by hearing members 32 and 34, whichbearing members when threaded in place in base 10 compress (i-ring seals36 and 3 8 to provide a fluid-tight seal between the base 1d and shaft28. Shaft 28 includes an eccentric portion 40, which preferably isground flat on one side of that portion of the shaft which extendswithin the hollow portion .343 of base 10. Ring 42, which encompassesthe shaft 28, includes a corresponding flat area 44 which mates with theeccentric flat area of shaft 28 when the ring is urged in a downwarddirection, as by tension applied to rod 46, which is secured to ring 42on the side thereof opposite from the aforesaid flat area. Rod 45terminates at eye 48, which eye is adapted to receive a test coil-spring50. Spring 5% is secured to the eye of rod 46 at one end, and toeye-bolt 24 at the other end, and is tensioned therebetween. Spring Stis preferably a helical coil-spring of uniform diameter fabricated of aferrous alloy, the embrittlernent characteristics of which are to bedetermined. When spring 58 is tensioned, as by rotation of nut 26, theflat areas of ring 42 and shaft 28 cooperate to impede rotation of shaft28. Externally of the base 10 an eccentric signalling device, whichincludes ring 52, rod 54, and signal flag 56-, is supported from shaft28. The weight and length of rod 54 are suflicient to compel, underforce of gravity, rotation of shaft 28 when notension is applied to rod45 by spring 56.

The device may readily be assembled and disassembled by means of thethreads 1-4 and 18, to insert and remove test springs. When assembled,nut 26 is rotated to provide the desired tension to spring 50, and thedevice inserted in a vessel containing the environment to be studied, asby screwing the base in place by means threads of 58, which are adaptedto mate with standard pressure-vessel fittings. Tension in spring 56retains shaft 28 in the angular position shown, against the torqueapplied by the weight of rod 54.

In use, after an appropriate period of exposure, for example 1 month,coil-spring 50 ruptures, releasing the downward force applied by ring 42to shaft 28. The shaft, then free to rotate, turns in bearings 32 and3d, and the flag drops from the horizontal to the vertical position,signalling failure of the spring. An advantage of the unitary design ofthe device of this invention is that none of the parts become disengagedfrom the device on the rupture of the spring, and therefore they cannotbe lost in the test fluid.

The spring 50, as aforestated, is fabricated of a ferrous alloy ofinterest. The remaining elements of the test assembly may be fabricatedof any desired material, but are preferably made of a non-ferrous alloyof high corrosion resistance to the fluid under study, as substantiallyall of the elements are exposed to the test fluid which may enter freelythrough the perforations of support 12. Suitable materials, which arenot subjectto hydrogen embrittlement, include brass, bronze, aluminum,and stainless steels. Chrome-plated steel elements may be used, or theprobe elements may be coated with a corrosion-impervious resin orplastic. Discretion should be employed in the selection of materials toprevent excessive corrosion which may develop due to galvanic cellaction between the ferrous coil-spring and other, uncoated, probeelements.

Referring to FIGURE 4, an alternate test structure is shown. Base 70 isa bull-plug, provided with an axial, stepped hole 72, which includesshoulders at 74, 76, and 7 8. Rod 80', which passes axially through hole72., terminates at one end at eye 82, and at the other end with threadedportion 84. A screwdriver slot 86 may be provided in the threaded end ofrod 8%. The rod is supported by hearing plug 88, which compresses anO-ring seal 90 between shoulder 78 and rod 80, to provide a sealtherebetween. Support rods 92 are pressed into the lower end ofbase 70,which is adapted for exposure to the test environment. These rodsprovide an anchor for the lower end of a test coil-spring, the upper endof the spring being secured to eye 82 of rod 8t A second coil-spring 4lies in the annular recess 95 between rod 80 and the interior side wallof base '70. This coilspring bears upward against signal block 96, whichencompasses a part of the threaded portion 84 of rod 80, and is securedagainst upward movement along the red by nut 98. Enlarged recess 100 inthe base 70 accommodates signal block 96, when rod 80 is urgeddownwardly by the tension of the test coil-spring, not shown. Adjustmentof the spring tension in the test spring may be accomplished by rotationof nut 98. Screwdriver slot 86 provides one expedient by which undesiredrotation of rodStt may be prevented while nut 98 is rotated.Alternatively, the rod may be keyed to the base 70. As nut 98 istightened, rod 80' is drawn upward until tension is applied to the testspring. Further rotation of nut 98 draws signal block 96 down intorecess 100, due to the fact that spring 94 is of relatively smallcrosssection and therefore readily compressed. Movement of signal block96 is halted when the lower surface 102 of the block strikes shoulder76. Further rotation of nut 98 raises rod 80, tensioning the testcoil-spring.

the test environment. Thus, a spring tension at a value lower than thecritical value for the ferrous alloy from which it is fabricated can beretensioned to a higher value by rotation of nut 98. This retensioningcan be done periodically until the critical value of stress has beenexceeded, and the spring ruptures. In this manner the critical stressfor the ferrous alloy under study can be bracketed.

It is preferred that the threads of both eye-bolt 24 of FIGURE 1, and ofrod of FIGURE 4, be cut with a pitch which is a convenient fraction ofan inch, such as 10 threads per inch. Thus,for example, one completerotation of nut 98, or nut 22, will apply a stretch of of an inch to thespring. If it is desire-d to stress the test spring to any desiredvalue, the testspring deflection corresponding to this stress can becalculated in a conventional manner, and the nut rotated until tensionis first felt to be applied to the spring. The nut may then be rotatedthe necessary number of times to deflect the spring through a distancewhich will apply to the desired stress. It is for this reason thatthreads having a pitch of 10 to the inch are most con venient.

The embodiments of the invention in which an exclusive property orprivilege is claimed are defined as follows:

1. An embrittlement-detection probe comprising a base adapted to matewith an opening in a test-environmentconfining wall to provide a firstportion of said base exposed to said environment and a second portionnot so exposed, a support member secured to said first portion of saidbase and projecting therefrom, signaling means associated with said basefor supporting one end of a coil-spring adjacent said first portion ofsaid base, and a ferrous coil-spring supported at one end by saidsignaling means and at the other end by said projecting support member,said signaling means being operable to produce a visible signal adjacentsaid second portion of said base in response to the breaking of saidspring.

2. An apparatus according to claim 1 in which said signal is the changeof position relative to said base of a member retained in position bythe tension of said spring prior to the breaking thereof.

3. An apparatus in accordance with claim 2 in which said base isthreaded for insertion in a pressure-vessel fitting.

4. An apparatus in accordance with claim 2'in which said first portionof said base is hollow and said signaling means comprises an eccentricshaft extending transversely of said spring through said base and thehollow portion thereof, means for applying rotative torque to saidshaft, and a link connecting said spring and the eccentric portion ofsaid shaft whereby tension in said spring restrains rotation of saidshaft. 1 I

5. An apparatus in accordance with claim 4 wherein said means forapplying torque comprises a weight supported radially of said shaft andexternally of said base.

6. An apparatus according to claim 1 in which said base includes anaperture extending therethrough and communicating with said secondportion thereof, said aperture being substantially coaxial with saidspring and said signaling means comprising a rod adapted at one end tosupport one end of said coil-spring slidably disposed within saidaperture, means limiting the movement of said rod towards saidcoil-spring, and means urging said rod in the direction to project fromsaid second portion of said base.

7. An apparatus in accordance with claim 6 including means for forming aseal between said rod and said aperture.

8. An apparatus in accordance with claim 7 including a recess in saidsecond portion of said base disposed radially of said. aperture, asignal block adapted to fit within said recess and encompassinga portionof said rod, said rod having a threaded portion at the end thereofopposite from the end adapted to support said coil- 6 spring, nut meanscooperating with said threaded portion References Cited in the file ofthis patent for limiting axial movement of said signal block rela-UNITED STATES PATENTS tive to said rod, and a coil-spring disposedcoaxially with said rod, bearing against said base and said signal2,283,954 Schroeder et a1 May 26, 1942 block to urge said signal blockoutward from said recess. 5 2,972,248 Garhardt 1961

1. AN EMBRITTLEMENT-DETECTION PROBE COMPRISING A BASE ADAPTED TO MATEWITH AN OPENING IN A TEST-ENVIRONMENTCONFINING WALL TO PROVIDE A FIRSTPORTION OF SAID BASE EXPOSED TO SAID ENVIRONMENT AND A SECOND PORTIONNOT SO EXPOSED, A SUPPORT MEMBER SECURED TO SAID FIRST PROTION OF SAIDBASE AND PROJECTING THEREFROM, SIGNALING MEANS ASSOCIATED WITH SAID BASEFOR SUPPORTING ONE END OF A COIL-SPRING ADJACENT SAID FIRST PORTION OFSAID BASE, AND A FERROUS COIL-SPRING SUPPORTED AT ONE END BY SAIDSIGNALING MEANS AND AT THE OTHER END BY SAID PROJECTING SUPPORT MEMBER,SAID SIGNALING MEANS BEING OPERABLE TO